Hard wear-resistant ferrous alloy

ABSTRACT

A hard, wear-resistant ferrous alloy of from 3.30 to 3.90 weight percent carbon, 0.75 to 1.25 weight percent boron, 1.20 to 1.60 weight percent manganese, 0.65 to 1.10 weight percent silicon, 4.10 to 5.00 weight percent nickel, 0.90 to 1.40 weight percent chromium, up to 0.50 weight percent molybdenum, and the balance essentially iron. The alloy is centrifugally cast into linings for extruders or injection molders for plastic materials, which linings possess improved hardness characteristics.

United States Patent Saltzman 51 Apr. 25, 1972 [54] HARD WEAR-RESISTANT FERROUS ALLOY [52] U.S.Cl. ..75/l28F, 75/128 C, 75/128R [51] Int. Cl [58] Field of Search [56] References Cited UNITED STATES PATENTS 2,066,848 1/1937 Merica ..75/l28D Primary Examiner-Hyland Bizot Attorney-0strolenk, Faber, Gerb & Soffen [5 7] ABSTRACT A hard, wear-resistant ferrous alloy of from 3.30 to 3.90 weight percent carbon, 0.75 to 1.25 weight percent boron, 1.20 to 1.60 weight percent manganese, 0.65 to 1.10 weight percent silicon, 4.10 to 5.00 weight percent nickel, 0.90 to 1.40 weight percent chromium, up to 0.50 weight percent molybdenum, and the balance essentially iron. The alloy is centrifugally cast into linings for extruders or injection molders for plastic materials, which linings possess improved hardness characteristics.

7 Claims, No Drawings HARD WEAR-RESISTANT FERROUS ALLOY BACKGROUND OF THE INVENTION The present invention relates to a wear-resistant ferrous alloy having improved hardness characteristics, and more particularly to such an alloy desirable for use as a lining for catalytic crackers, plastic extruders, Banbury mixers or other devices requiring hard, wear-resistant linings.

Bimetallic cylinders having centrifugally cast wear-resistant ferrous alloy linings are commonly used for heating, mixing and pressurizing plastic materials in extruders and injection molding equipment. Alloys so useful may principally consist of iron containing carbon in amounts of from 2 to 4 percent by weight, boron in amounts of from 0.2 to 2.5 percent by weight, and nickel in amounts of from about 1.5 to 9 percent by weight, although minor proportions of additional metals such as chromium, tungsten, manganese, vanadium, molybdenum, cobalt, etc. may also be tolerated therein. Such alloys and bimetallic cylinders manufactured by the centrifugal casting thereof are described, for example, in Kormann et al. U.S. Pat. Nos. 2,046,913 and 2,046,914 granted on July 7, 1936 and assigned to the predecessor of the assignee of the present invention.

Ferrous alloy linings of the type described in the Kormann et al. patents have typical room temperature hardness characteristics of from 58 to 64 Rockwell C in the as centrifugally cast (as-spun) condition. The surfaces of such alloy linings provide superior resistance to wear during operation of the extruder or injection molder incorporating the same. Such wear may, for example, result from abrasive fillers present in the plastic material to be extruded or molded, or from pressures produced by the feed screw of the device bearing against the cylinder under abnormal operating conditions.

Operating temperatures for plastic extrusion and injection molding generally range from about 400 to 650 F., and may be as high as 800 F. for certain materials. Extruder or injection molder cylinder linings must, therefore, possess excellent hot hardness characteristics in addition to other wear-resistant properties. Under abnormal operating conditions, for example when heater controls fail to operate or when, as indicated above, the feed screw bears against the cylinder walls, such a lining material may even be locally exposed to temperatures markedly higher than those specified above which are normally encountered in practice. Such elevated temperature exposure may reduce the subsequent room temperature hardness of the alloy lining, leaving areas of reduced hardness which may be subject to failure.

The alloy linings of the materials generally described in the aforesaid Kormann et al. patents possess hot hardness characteristics which are adequate for most applications in extruders and injection molders for plastic materials. They do, however, exhibit slowly decreasing hardnesses up to approximately 700 F. Moreover, when exposed to temperatures above 800 F., such lining materials exhibit considerably reduced hot hardness characteristics and, subsequent to elevated temperature exposure, markedly decreased room temperature hardnesses.

It is, therefore, a principal object of the present invention to provide a wear-resistant ferrous alloy useful as a lining for bimetallic cylinders of the type discussed hereinabove which possesses improved high temperature hardness characteristics and which exhibits greater retention of hardness after exposure to elevated temperatures. Other objects and advantages of the invention will be more fully apparent from a consideration of the following detailed description of preferred embodiments thereof; in such description, and in the claims appended hereto, all parts and percentages are given by weight and all temperatures are in degrees Fahrenheit unless otherwise specified.

SUMMARY OF THE INVENTION The ferrous alloy of the present invention comprises the fol lowing elements fused together in approximately the proportions stated below:

Ingredient Weight Percent Carbon 3.30 to 3.90 Boron 0.75 to 1.25 Manganese 1.20 to 1.60 Silicon 0.65 to 1.10 Nickel 4.10 to 5.00 Chromium 0.90 to 1.40 Molybdenum Up to 0.50

Iron, balance to make up The expression up to" a specified percentage is intended to include 0 percent of the indicated component.

It has been found that centrifugally cast linings of the ferrous alloys of the above compositions possess significantly higher hot hardness characteristics at temperatures up to 700 to 800 F., and significantly lower losses in room temperature hardness after exposure to temperatures of from about 800 to l,300 F., as compared with previously known hard, wear-resistant ferrous alloys. In particular, it appears that the addition of the specified proportions of chromium and, possibly, molybdenum to the alloy composition provides bimetallic cylinder linings which exhibit these superior characteristics. For example, alloy linings prepared from the composition of Example 3 below have Rockwell hardnesses (Rc) at 500 of 62.3 whereas linings prepared from a composition which has previously been commercially used and which is within the scope of the previously discussed Kormann et al. patents (control A described below, having a composition incorporating 3.67 percent carbon, 1.06 percent boron, 1.42 percent manganese, 0.92 percent silicon, and 4.35 percent nickel) possess a comparable hardness of only 56.4 (see Table III below). Similarly, the room temperature hardness of linings of the composition of Example 3 is Rc 58.2 after exposure to a l,200 elevated temperature for 4 hours, whereas the comparable hardness exhibited by the above mentioned control composition is only Rc 47.8.

The ferrous alloys hereof are, as indicated above, preferably employed in the formation of liners for various devices requiring hard, wear-resistant material contacting surfaces. Such linings may, for example, be formed on either the interior or exterior surfaces of cylindrical ferrous metal shells and the desired devices fabricated therefrom, e.g., asdescribed in the aforesaid Kormann et al. U.S. Pat. No. 2,046,914, as well as in U.S. Pat. Nos. 2,275,503, 2,319,657 and 3,254,381.

One mode of manufacturing wear-resistant linings in accordance with the present invention involves charging the alloy composition into the region in which a lining is to be formed, e.g., into the interior of a tubular steel housing. The alloy composition may previously be fused and charged in shot form or in cast and crushed form into the tubular housing.

After capping the ends of the tubular steel housing to containthe charged alloy and prevent atmospheric oxidation, the unit is placed in a furnace, frequently'in admixture with a flux to prevent oxidation, and heated at a temperature of from about 2,000 to 2,300 F. to melt the components. After heating the sealed tube to above the melting point of the alloy composition, i.e., from about 2,000 to 2,300 F., for up to 2 hours (depending on the size of the tube), the assembly is removed from the furnace and spun to centrifugally form the alloy lining.

The assembly is rapidly cooled during the spinning operation, e.g., within about 10 minutes, to temperature of about 1,700 F. The assembly is thereafter covered with a suitable insulating material, e.g., sand, diatomaceous earth or silica, and permitted to cool over a period of from about 24 to 48 hours to temperatures within the range of from about 300 to 500 F. The alloy melt is thus fused and metallurgically bonded to the steel housing. The caps are thereafter removed from the ends of the housing and the internal and external diameters desired are finished in customary manner.

PREFERRED EMBODIMENTS OF THE INVENTION The following examples illustrate particularly preferred compositionsof the hard, wear-resistant ferrous alloys of the present invention, and compare the hardness characteristics of two such alloy compositions with those exhibited by various control materials.

Hard, wear-resistant ferrous alloy compositions within the scope of the present invention, identified as Examples l-3, were prepared by mixing calculated portions of pig iron and the various alloying ingredients, followed by melting and fusing the same. Various control compositions, identified as controls A-E, were similarly prepared, control A corresponding to a composition commercially used for bimetallic tubular linings in accordance with the above mentioned Kormann et al. patents and controls B-E otherwise varying from the composition of the alloys of this invention. The various alloy compositions were air melted in a 20 KW Ajax-Magnethermic induction furnace and cast into waffle plate molds. Each waffle plate was broken up into approximate l-inch squares for loading in steel cylinders, nominally 1% inches I.D. X 3 inches O.D. X 2 feet length, for production of centrifugally cast linings. The analyses of the respective alloy compositions of Examples l-3 and controls A-E, as loaded for centrifugal 2 casting, are set forth in Table 1 below.

Squares of the respective alloys were charged within steel tubes, heated and spun in the manner described hereinabove. The bores of the bimetallic cylinders thus produced were honed to provide smooth internal surfaces.

For test purposes, rings were cut from the cylinders incorporating linings of the alloys of Examples 2 and 3 and controls A-E. Waffle plates from which the linings were prepared and the lining ring specimens themselves were examined metallographically and the following hardness measurements made on the respective lining samples. First, the room temperature hardnesses of the several lining samples, as spun, were determined. The samples were then heated at 1,500 F. for l or 4 hours (the time of heating was found immaterial) and air. cooled, after which the average room temperature hardnesses were again determined. The as-spun and heat treated room temperature hardness characteristics of the various inlay samples are set forth in Table 11 below.

Further test specimens of the alloy linings of Examples 2 and 3, and controls B-E, cubes approximately three-fourth 40 inch per side, were also subjected to hot hardness tests. In these tests the hardness of each specimen was determined during exposure to temperatures of 300, 500, 700, 900, l,00O, 1,100 and l,200, respectively. The comparable hot hardness values for the commercially employed material of control A were taken from previously published data. The hot hardness characteristics thus determined are tabulated in Table III below.

Finally, further samples of the respective alloy linings of Examples 2 and 3 and controls A-E were subjected to tests to 5() determine the effect of elevated temperature exposure on room temperature hardness. The samples were first heat treated at l,500 F. followed by air cooling; they were then exposed for periods of 4 hours at varying temperatures differing by 100 increments within the range of from 600 to l,400 F., and again air cooled. The changes in the room temperature hardnesses were then determined. The hardnesses of the several test samples at the various exposure temperatures are tabulated in Table IV below.

It is apparent from Table 11 that the as-spun room temperature hardnesses of the alloy linings varied considerably from one another, whereas the variations in room temperature hardness characteristics after heat treating were much TABLE I.CHEMICAL COMPOSITION OF CEN'IRIFUGALLY CAST ALLOYS Weight percent Alloy C B Mn Si N1 M0 V Cr Fe Exumplul 3.75 0.76 1.3-1 0.77 4.45 1.17 Bill. l lxlllllpltll 3.81 1.06 1.31) 0.78 4.02 0. 18 1.18 Ilnl. l ltnmplu .1 3. Hi) l.0 l 1.15 0. (l5 -1. .10 1.21 llul. ttmlml it u. l ml 1.4; 0 tr. rzm llul. lnltliul l\ .l ill! I Ill 1 1'5 1 Ill 1.60 11,41) l).',"- lllll. l'nllll'ol l .Til (H l IL!" 5.37 ".Hll "Jill lltll. (null-til l) ILM LII? 1.118 1.78 H 0.55 llul. \uulml l". l. 5.53 0. 50 llnl.

TABLE ll ROOM TEMPERATURE HARDNESS OF CENTRIFUGALLY CAST LlNlNGS Average Hardness (Re) Alloy As Spun Heat Treated Example 2 63.0 65.7 Example 3 63.5 65.6 Control A 57.1 65.7 Control B 62.3 66.9 Control C 61.5 65.5 Control D 63.5 65.0 Control E 62.8 65.3

TABLE IIl.-IIOT HARDNESS OF CENTRIFUCALLY CAST ALLOYS Hardness (Re) TABLE IV.EFFECT OF ELEVATED TEMPERATURE EX- POSURE ON THE ROOM TEMPERATURE HARDNESS OF OENTRIFUGALLY CAST ALLOYS Hardness (Re) Example Control Exposure temp.

( F.) 2 3 A B C D E 62. 0 61. 2 62. 7 59. 3 5S). 9 61. 6 61.1 61. 8 60. 6 60.8 57. 9 59. 1 58. 9 58. 8 58. 0 58.6 54.1 59. 2 58.5 57.5 57.8 57. 4 51. D 57. 5 55.8 54. 6 55. 3 51.7 48.0 54. 5 54.1 57.0 53. 7 58. 2 47. 8 58.4 57.0 60. 5 57. f) 64.0 60. 0 61. 7 62. 8 64. 5 64. 3 66. 5 65. 3 66. 2 66. 0 65.7 65.8

smaller. The difference between the as-spun hardness of Examples 2 and 3 as compared with that of control A is, however, quite significant. Metallographic examination of the control A inlay indicated that such difference was due to a relatively high proportion of bainite in the structure thereof. The modified alloys of the present invention thus exhibit a greater hardenability than alloys of this prior commercial type.

It may be seen from the hot hardness test results given in Table III that the alloys of the present invention (Examples 2 and 3) have hardnesses of Rc 60 or greater at temperatures up to about 500 F. On the other hand, the composition of control A has a hot hardness of less than Re 58 above about 300 F. Similarly, control alloys C-E have hardnesses of less than RC 60 above about 300 F. The hardness characteristics of the several alloy compositions drop rapidly above 500; however, it will be noted that the hardnesses of the compositions of Examples 2 and 3 are markedly superior to those of controls A, C, D and E at each of the temperature levels up to l,200 F and superior to control B at temperatures within the range of from 300 to 700. Moreover, the alloys of Examples 2 and 3 retain hot hardnesses of Re 58 to above 600 F.

As shown in Table IV, exposure to increased temperature has marked effects on the subsequent room temperature hardness characteristics of the various test alloys. Thus, the previously known composition of control A has a room temperature hardness of less than Re 58 tiller exposure in temperatures above 800" F. Controls C, D and E retain room temperature hardnesses of Re 58 or greater after exposure up to 850 to 925. The alloys of Examples 2 and 3 and control B retain hardnesses of Rc 58 or greater after exposure to 950, but the latter material exhibits decreased hardness characteristics relative to the compositions of Examples 2 and 3 after exposure to temperatures of the order of l,300 F. In particular, the alloys of the present invention exhibit marked superiority over the previously employed alloy of control A throughout the temperature range of from 800 to 1,300 E, the alloy of Example 3 having room temperature hardnesses of from 2.9 to 10.3 Rockwell-C points greater than those for control A after exposure at temperatures throughout the noted range.

It may thus be seen that, in accordance with the present invention, a ferrous alloy having improved hardness characteristics may be produced. Since various changes may be made in the specific embodiments of the alloy, its preparation and its mode of use without departing from the scope of the invention, it will be understood that the preceding description is intended as illustrative and not in a limiting sense.

1 claim:

1. A hard, wear-resistant ferrous alloy consisting essentially of the following ingredients fused together in approximately the proportions stated below:

ingredient Weight Percent Carbon 3.30 to 3.90 Boron 0.75 to 1.25 Manganese 1.20 to 1.60 Silicon 0.65 to 1.10 Nickel 4.10 to 5.00 Molybdenum Up to 0.5 Chromium 0.90 to 1.40

lron. balance to make up 100%.

2. The hard, wear-resistant ferrous alloy of claim 1, consisting essentially of the following ingredients fused together in approximately the proportions stated below:

lngredient Weight Percent Carbon 3.81 Boron 1.06 Manganese 1.39

Silicon 0.78 Nickel 4.92 Molybdenum 0.48 Chromium l l 8 Iron, balance to 3. The hard, wear-resistant ferrous alloy of claim 1, consisting essentially of the following ingredients fused together in approximately the proportions stated below:

Iron. balance to 100%.

l 4. The hard, wear-resistant ferrous alloy of claim 1, consisting essentially of the following ingredients fused together in approximately the proportions stated below:

lngredient Weight Percent Carbon 37 5 Boron 0 7 Manganese 1.34 Silicon 0.77 Nickel 4,45 Chromium 1 7 lron, balance to 100%.

5. A hard, wear-resistant liner for a steel housing, constituted of the ferrous alloy of claim 1.

6. A hard, wear-resistant liner for a steel housing, constituted of the ferrous alloy of claim 2.

7. A hard, wear-resistant liner for a steel housing, constituted of the ferrous alloy of claim 3. 

2. The hard, wear-resistant ferrous alloy of claim 1, consisting essentially of the following ingredients fused together in approximately the proportions stated below: Ingredient Weight Percent Carbon 3.81 Boron 1.06 Manganese 1.39 Silicon 0.78 Nickel 4.92 Molybdenum 0.48 Chromium 1.18 Iron, balance to 100%.
 3. The hard, wear-resistant ferrous alloy of claim 1, consisting essentially of the following ingredients fused together in approximately the proportions stated below: Ingredient Weight Percent Carbon 3.80 Boron 1.04 Manganese 1.45 Silicon 0.65 Nickel 4.99 Chromium 1.21 Iron, balance to 100%.
 4. The hard, wear-resistant ferrous alloy of claim 1, consisting essentially of the following ingredients fused together in approximately the proportions stated below: Ingredient Weight Percent Carbon 3.75 Boron 0.76 Manganese 1.34 Silicon 0.77 Nickel 4.45 Chromium 1.17 Iron, balance to 100%.
 5. A hard, wear-resistant liner for a steel housing, constituted of the ferrous alloy of claim
 1. 6. A hard, wear-resistant liner for a steel housing, constituted of the ferrous alloy of claim
 2. 7. A hard, wear-resistant liner for a steel housing, constituted of the ferrous alloy of claim
 3. 